with Formula for ascertaining its power. 257 



It would be extremely interesting to find every case of de- 

 composition of a compound fluid obedient to the equation, and 

 indeed there is every appearance of that being the fact. 



The impossibility of giving a negative tendency to a metal 

 when hydrogen is removed from its surface is also perfectly 

 accounted for by our equation ; for hydrogen, as has been al- 

 ready shown, protects the metal ; so when a facility is offered 

 for its removal, not only is the direct protection removed, but 

 by diminishing the value of [e), (F) the natural affinity of the 

 metal for one element of the fluid, having but little resistance 

 opposed to it, begins to act, and the metal is therefore dissolved. 



The superior action of a rough metal in contrast with a 

 smooth one, is explainable on the equation most satisfactorily, 

 for in the first case the affinity (F) is but feebly opposed by the 

 resistance to the evolution of the hydrogen (e) t whilst in the 

 latter case (F) is so strongly opposed by (e) that no action can 

 take place. Zinc shavings, which always have one side bright 

 and the other rough, show this phenomenon clearly. Polished 

 zinc or iron also show this effect in a striking manner. 



Hitherto we have considered (F, a, c,r,e) in every case to 

 be constant, but in many instances they are subjected to con- 

 tinual variation. I do not, indeed, happen to recollect an in- 

 stance of (F) varying to any amount, but (a) varies frequently ; 

 in the gradual saturation of a fluid it progressively increases, 

 so much so, as at last to equal (F). This accounts for zinc 

 ceasing to be dissolved on the saturation of the fluid by sul- 

 phate of zinc, although still intensely acid, (c) generally re- 

 mains constant, (r) is very unsteady, for as in all voltaic ar- 

 rangements the fluid is always undergoing change, it is there- 

 fore sure to be altered in its conducting power, (e) is sub- 

 ject to great variations from alteration of the liquid and other 

 causes. 



In every case of a single battery we have seen that the in- 

 tensity is equal to chemical affinity, minus the resistances to 

 that affinity. In a compound battery the expression is equally 

 simple, for the intensity is equal to the sum of the affinities, 

 minus the sum of the resistances. In a series of batteries all 



of the same nature, V = F-a+c+r + fx». Sometimes (») 

 is very complex. For example, if a compound battery be 

 made up of a Grove's, a DanielPs, and my own, the values of 

 (I) must be considered separately, and their sum taken. 



The diagram exhibits well the arrangement and properties 

 of the compound battery. 



A good example of the effect of (n) is seen in the water 

 battery, where (I) is exceedingly small from the resistances 



Phil. Mag. S. 3. Vol. 21. No. 1 38. Oct. 1842. S 



